* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
  }
  
  body {
    font-family: Arial, sans-serif;
    background-color: #f8f9fa;
    transition: background-color 0.5s ease; /* 平滑的背景颜色过渡 */
  }
  
  header {
    background-color: #333;
    padding: 30px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
  header h1 {
    color: white;
    margin: 0;
    font-size: 32px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
  header nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
  }
  
  header nav ul li {
    margin-left: 40px;
  }
  
  header nav ul li a {
    color: white;
    text-decoration: none;
    transition: color 0.3s ease;
    font-size: 20px;
  }
  
  header nav ul li a:hover {
    color: #ffc107;
    transform: scale(1.1); /* 鼠标悬停时放大链接 */
    transition: all 0.3s ease; /* 平滑的缩放过渡 */
  }
  
  #search-box {
    padding: 20px;
    border: 2px solid #ffc107;
    border-radius: 15px;
    width: 500px;
    font-size: 18px;
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.2);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
  main {
    padding: 40px;
    box-shadow: 0 0 20px rgba(0, 0, 0, 0.1);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .slider {
    width: 100%;
    height: 700px;
    overflow: hidden;
    position: relative;
    border-radius: 20px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .slide {
    width: 100%;
    height: 100%;
    position: absolute;
    opacity: 0;
    transition: opacity 0.5s ease-in-out;
  }
  
 .slide.active {
    opacity: 1;
    transform: scale(1.05); /* 激活的幻灯片略微放大 */
    transition: all 0.5s ease; /* 平滑的缩放过渡 */
  }
  
  img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.5s ease; /* 平滑的图片变换过渡 */
  }
  
 .slider-controls {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    width: 100%;
    display: flex;
    justify-content: space-between;
    padding: 0 50px;
  }
  
 .slider-controls button {
    background-color: rgba(0, 0, 0, 0.7);
    color: white;
    border: 3px solid white;
    padding: 20px 40px;
    cursor: pointer;
    font-size: 40px;
    opacity: 0.8;
    transition: opacity 0.3s ease, background-color 0.3s ease; /* 平滑的透明度和背景颜色过渡 */
  }
  
 .slider-controls button:hover {
    opacity: 1;
    background-color: rgba(255, 193, 7, 0.7); /* 鼠标悬停时更改背景颜色 */
    transition: all 0.3s ease; /* 平滑的过渡 */
  }
  
 .slider-indicators {
    position: absolute;
    bottom: 50px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    gap: 20px;
  }
  
 .slider-indicators button {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background-color: rgba(255, 255, 255, 0.5);
    border: 3px solid white;
    cursor: pointer;
    transition: background-color 0.3s ease;
  }
  
 .slider-indicators button.active {
    background-color: white;
    transform: scale(1.2); /* 激活的指示器放大 */
    transition: all 0.3s ease; /* 平滑的过渡 */
  }
  
 .course-category {
    background-color: #007bff;
    color: white;
    padding: 25px 40px;
    margin-bottom: 40px;
    font-size: 26px;
    border-radius: 15px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.2);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .course-card {
    background-color: white;
    border: 3px solid #007bff;
    padding: 40px;
    margin-bottom: 40px;
    box-shadow: 0 10px 20px 0 rgba(0, 0, 0, 0.1);
    transition: 0.3s;
    display: flex;
    align-items: center;
    border-radius: 20px;
    cursor: pointer; /* 使卡片可点击 */
  }
  
 .course-card:hover {
    box-shadow: 0 20px 40px 0 rgba(0, 0, 0, 0.2);
    transform: translateY(-10px); /* 鼠标悬停时向上移动 */
    transition: all 0.3s ease; /* 平滑的过渡 */
  }
  
 .course-card img {
    width: 300px;
    height: 250px;
    object-fit: cover;
    margin-right: 40px;
    border-radius: 15px;
    transition: transform 0.5s ease; /* 平滑的图片变换过渡 */
  }
  
 .course-card h3 {
    margin: 0;
    font-size: 28px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .course-card p {
    margin: 20px 0 0 0;
    font-size: 18px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .course-card.rating {
    color: #ffc107;
    margin-top: 20px;
    font-size: 20px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .course-reviews {
    margin-top: 20px;
    color: #888;
    font-size: 18px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .course-details {
    padding: 50px;
    background-color: rgba(255, 255, 255, 0.9);
    border-radius: 20px;
    box-shadow: 0 10px 20px 0 rgba(0, 0, 0, 0.1);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .course-details h2 {
    margin-top: 0;
    font-size: 32px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .course-details p {
    margin-top: 25px;
    font-size: 20px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .recommended-courses {
    margin-top: 50px;
  }
  
 .recommended-courses h3 {
    margin-bottom: 25px;
    font-size: 26px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .recommended-course-card {
    border: 3px solid #ddd;
    padding: 25px;
    margin-bottom: 25px;
    border-radius: 15px;
    background-color: rgba(255, 255, 255, 0.8);
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.05);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .recommended-course-card img {
    width: 150px;
    height: 120px;
    object-fit: cover;
    margin-right: 20px;
    border-radius: 8px;
    transition: transform 0.5s ease; /* 平滑的图片变换过渡 */
  }
  
 .recommended-course-card h4 {
    margin: 0;
    font-size: 20px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .recommended-course-card p {
    margin: 10px 0 0 0;
    font-size: 16px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .user-comment {
    background-color: #f1f1f1;
    padding: 30px;
    margin-bottom: 30px;
    border-radius: 15px;
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.05);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .user-comment h4 {
    margin: 0 0 15px 0;
    color: #333;
    font-size: 20px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .user-comment p {
    margin: 0;
    font-size: 18px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .course-video-preview {
    width: 100%;
    height: 500px;
    background-color: #333;
    margin-top: 50px;
    border-radius: 15px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.2);
    transition: box-shadow 0.5s ease; /* 平滑的阴影过渡 */
  }
  
 .instructor-card {
    background-color: white;
    border: 3px solid #ddd;
    padding: 40px;
    margin-bottom: 40px;
    box-shadow: 0 10px 20px 0 rgba(0, 0, 0, 0.1);
    transition: 0.3s;
    display: flex;
    align-items: center;
    border-radius: 20px;
    cursor: pointer; /* 使讲师卡片可点击 */
  }
  
 .instructor-card:hover {
    box-shadow: 0 20px 40px 0 rgba(0, 0, 0, 0.2);
    transform: translateY(-10px); /* 鼠标悬停时向上移动 */
    transition: all 0.3s ease; /* 平滑的过渡 */
  }
  
 .instructor-card img {
    width: 200px;
    height: 200px;
    border-radius: 50%;
    object-fit: cover;
    margin-right: 40px;
    transition: transform 0.5s ease; /* 平滑的图片变换过渡 */
  }
  
 .instructor-card h3 {
    margin: 0;
    font-size: 28px;
    transition: color 0.5s ease; /* 平滑的颜色过渡 */
  }
  
 .instructor-card p {
    margin: 20px 0 0 0;
    font-size: 18px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
 .instructor-card.courses-taught {
    margin-top: 20px;
    color: #888;
    font-size: 18px;
    transition: opacity 0.5s ease; /* 平滑的透明度过渡 */
  }
  
  @media (max-width: 768px) {
    header h1 {
      font-size: 26px;
    }
  
    header nav ul li {
      margin-left: 20px;
    }
  
    header nav ul li a {
      font-size: 18px;
    }
  
    #search-box {
      width: 350px;
    }
  
   .slider-controls button {
      font-size: 32px;
    }
  
   .course-card {
      flex-direction: column;
      align-items: stretch;
    }
  
   .course-card img {
      width: 100%;
      height: 300px;
      margin-right: 0;
      margin-bottom: 20px;
    }
  }
  header a.btn {
    padding: 18px 30px;
    border-radius: 25px;
    font-size: 20px;
    transition: background-color 0.3s ease, transform 0.3s ease;
}

header a.btn-secondary {
    background-color: #6c757d;
    color: white;
}

header a.btn-success {
    background-color: #28a745;
    color: white;
}

header a.btn:hover {
    transform: scale(1.1);
}
 